Basics of Nonlinear Optics

The fields of nonlinear optics (NLO) and laser physics and technology are intertwined. Research and development made in respective subject areas have benefited each other for their further advancement. The field of NLO therefore continues to be an active and rapidly developing research area. The aim of this chapter is to provide brief account of the basics of NLO with the description of some of the well-known NLO processes and phenomena. We consider classical treatment of light-matter interaction and restrict to dipolar polarization induced by the field in the material. We discuss various novel optical effects and phenomena due to induced second and third order nonlinear polarization in the medium. These novel effects include photon-photon interaction leading to exchange of energy among light beams and with medium excitations, generation of coherent light sources at new frequencies, modulation and control of light beam amplitude and phase, etc.